The present invention relates to a portable device (a bin system) for metering and delivering a desired weight of a cohesive particulate solid material such as pigmentary titanium dioxide.
Solid, powder materials are generally delivered to an industrial user as large bulk volumes such as hopper cars or truck, as shipments of large single bags containing a ton or metric ton of material, or as pallets of individual bags, each weighing 50 pounds or more.
Often times in an industrial process, the manufacturer may need to add a small amount of solid powder to make or top off a batch of product. The weight needed may be too small to be conveniently delivered from a large bulk storage device or an amount that is not a convenient multiple of a small package of material, for example, a 50-pound bag.
Although prior art describes various schemes or devices for small bulk delivery of powders, no system has provided the accuracy or complete discharge of cohesive powders necessary to industrial processes.
U.S. Pat. No. 3,820,697 teaches a valve system for controlling the flow of fluids or easy-to-flow granules from a storage hopper. This valve system appears to be prone to possible jamming or leakage and contamination of the powder by the fluids actuating the valve.
U.S. Pat. No. 4,691,843 teaches a valve assembly which may be used on fixed or portable storage bins to discharge bulk solid materials, but this system has proved inadequate in the delivery of cohesive powders such as titanium dioxide as reported in the article by Bell and Grygo, Applications of Solid Flow Testing to Portable Bin Systems, published in the Proceedings of the Second Israel Conference for Conveying and Handling Particulate Solids, Jerusalem, May, 1997, pages 10.8 to 10.13.
Other patents relate to solids delivery systems are U.S. Pat. Nos. 4,378,897; 4,337,880; European Patent Application 0 197 342; U.S. Pat. No. 5,145,009 and European Patent EP 0 678 736 B1, but none of these teach or suggest a delivery or metering system for cohesive powders.
The present invention is a portable device (bin system) for delivery and metering of bulk cohesive powders comprising: (a) a hopper supported on a frame, wherein the hopper has an opening into which the bulk powder is charged formed by vertical walls and a section of generally converging walls connecting the vertical wall to an opening through which material is discharged wherein at least the portion of the hopper having converging walls is lined with a pneumatic fluidizing membrane; (b) a flow control mechanism; (c) a means of measuring and controlling the weight of material discharged; (d) a control loop to close the flow control mechanism when the desired weight has been discharged from the hopper; and (e) means to render the device portable; wherein the flow control mechanism is a valve assembly comprising a piston valve having a cone shaped closure member, a body comprising a cylinder of which the interior walls are lined with a pneumatic fluidizing membrane, an automatic means by which the valve is moved downward and upward between the open and closed positions and is optionally oscillated at selected amplitudes and frequencies about the opened position and a ring forming a valve seat wherein the ring has slots through which a flow of gas is directed.
The preferred automatic means by which the valve is moved downwards and upwards and optionally vibrated is a gas pressure regulated and controlled pneumatic controller.
The preferred means for metering the weight of material discharged are load cells positioned between the hopper and support frame.
To provide convenient delivery to a specific location, the device of the present invention may further comprise a discharge chute positioned below the flow control mechanism to direct the material discharged. With very cohesive powders, it is preferred that the discharge chute be lined at least on the lower inside surface with a pneumatic fluidizing membrane.
To reduce dusting, the device of the present invention may be fitted with a top-cover placed over the opening of the hopper wherein the top-cover is formed from a structural material or from fabric. Additionally, the device may be fitted with a paddle positioned on the valve closure member and extending into the hopper to aid in breaking up lumps of the powder.
The device of the present invention includes as a part of the device a means to render the device portable such as wheels or pockets to receive forklift arms.
The present invention also includes a method for adding a predetermined amount of a cohesive powder to an in-process product batch comprising discharging the cohesive particulate solid material from a bulk storage device into equipment processing the product batch wherein the bulk storage device comprises: (a) a hopper supported on a frame, wherein the hopper has an opening into which the bulk powder is charged formed by vertical walls and a section of generally converging walls connecting the vertical wall to an opening through which material is discharged wherein at least the portion of the hopper having converging walls is lined with a pneumatic fluidizing membrane; (b) a flow control mechanism; (c) a means of measuring and controlling the weight of material discharged; (d) a control loop to close the flow control mechanism when the desired weight has been discharged from the hopper; and (e) means to render the device portable; wherein the flow control mechanism is a valve assembly comprising a piston valve having a cone shaped closure member, a body comprising a cylinder of which the interior walls are lined with a pneumatic fluidizing membrane, an automatic means by which the valve is moved downward and upward between the open and closed positions and is optionally oscillated at selected amplitudes and frequencies about the opened position and a ring forming a valve seat wherein the ring has slots through which a flow of gas is directed.
The present invention also includes a valve assembly comprising a piston valve having a cone shaped closure member, a body comprising a cylinder of which the interior walls are lined with a pneumatic fluidizing membrane, an automatic means by which the valve is moved downward and upward between the open and closed positions and is optionally oscillated at selected amplitudes and frequencies about the opened position and a ring forming a valve seat wherein the ring has slots through which a flow of gas is directed.